1. Technical Field
The present invention relates to a magnetic recording apparatus and magnetic recording method.
2. Background Art
In magnetic recording apparatuses as represented by magnetic disc apparatuses, recording is carried out by forming a magnetic pattern corresponding to a recording signal in a magnetic recording medium. The recording pattern is formed by applying a recording magnetic field using a recording head. As shown in FIG. 10, a recording head 28 includes a high-permeability recording pole 29 with a coil 30 wound thereon. A recording current is supplied to the coil 30 from a recording driver circuit. The current flowing in the coil 30 magnetizes the recording pole 29 to produce a recording magnetic field, by which a recording pattern 31 is formed in a magnetic disc 32. The strength of the recording magnetic field produced by the recording head 28 and the profile of the magnetic field, as well as the magnetic characteristics of the recording medium, are important factors that determine many characteristics relating to recording performance, such as the readout signal intensity, signal-to-noise ratio, and overwrite performance. The recording magnetic field is dependent on the intensity and waveform of the recording current, in addition to the material and structure of the recording head pole. Thus, in order to realize high-density recording in an optimized manner, it is necessary to optimize not only the magnetic characteristics of the magnetic recording medium and the recording head structure, but also the amplitude and waveform of the recording current.
In the prior art, one of the requirements to be satisfied concerning the recording current has been the ensuring of a recording current amplitude such that the strength of the recording magnetic field that is generated exceeds the magnetic field with which a magnetization pattern can be formed in the recording medium. Another requirement has been the provision of an overshoot at the rise portion of the current so as to reduce the inversion time of the recording magnetic field. The overshoot in the current waveform causes the pole in the head to be more strongly magnetized upon magnetization inversion, so that the magnetization inversion can take place faster. The reduction in the inversion time of the recording magnetic field is effective in forming a sharper boundary in the recording pattern and is therefore suitable for high-density or high-frequency recording. Accordingly, the current waveform in the prior art, such as one described in U.S. Pat. No. 6,301,068, is made up of a combination of a current waveform having a constant amplitude with an overshoot at the rise portion thereof. In this case, recording is optimized by adjusting the amplitude of the overshoot at the rise portion and the amplitude of the subsequent constant current.
FIG. 11 schematically shows a conventional recording current driver circuit. FIG. 12 shows a chart with reference to which the recording current waveform will be described. As shown in FIG. 11, the driver circuit for generating the recording current waveform includes a constant current generating circuit 3 for supplying a recording current IwB having a constant amplitude ensuring the formation of a magnetization pattern, and an overshoot generating circuit 2 for generating an overshoot current waveform IwA. The two current waveforms are summed at a timing corresponding to a recording signal Vo generated by a recording signal generating circuit 1. The resultant current waveform is then fed to a recording head 4. A recording current waveform IwC for forming one recording pattern has an overshoot at the head, followed by a continuation of a certain level of current amplitude, as shown in FIG. 12. The waveform continues with its polarity inverted in accordance with the recording timing of the subsequent pattern.
JP Patent Publication (Kokai) No. 7-65303 A (1995) discloses a magnetic recording system using a ring head, in which a recording current waveform includes a time period with a reduced current amplitude prior to polarity inversion so that S/N during recording and reading can be enhanced.
(Patent Document 1) U.S. Pat. No. 6,301,068
(Patent Document 2) JP Patent Publication (Kokai) No. 7-65303 A (1995)